In long-term evolution (LTE), radio link failure (RLF) occurs when an user equipment (UE) in an RRC_connected state detects timer expiry due to downlink (DL) out-of-synchronization (out-of-sync or OOS) condition, random access procedure failure or radio link control (RLC) failure. In the case of timer expiry due to DL OOS condition, physical (PHY) sublayer sends a number of OOS indications and in-synchronization (in-sync or IS) indications to radio resource control (RRC) sublayer periodically, and RRC sublayer detects DL radio link problems when consecutive N1 of periodic OOS indications are received. Once receiving the consecutive N1 of the OOS indications from PHY sublayer, a timer T1 starts. The timer T1 will stop when receiving N2 of consecutive IS indications in RRC sublayer. If the timer T1 keep running until it expires, radio link failure will be confirmed and a timer T2 will start for initiating RRC connection re-establishment procedure if security is activated. If T2 expires due to RRC re-establishment failure, the UE would enter the RRC_idle state. If the timer T1 keep running until it expires and security is not activated, the UE would enter the RRC_idle state.
In new radio (NR), the UE is configured in communication with base stations via radio beams. The UE monitors associated reference signal for beam failure detection and the beam failure occurs when the beam failure condition is met based on the configured parameters, e.g., beamFailureInstanceMaxCount and beamFailureDetectionTimer. Beam failure recovery (BFR) can be performed to resolve the beam failure and restore the radio link so that the heavy RRC connection re-establishment can be avoided when the UE declares an RLF.
However, the RLF procedure and the BFR procedure are performed separately in different sublayers, resulting in radio link restoration time wasting and bad user experiences. Therefore, an interaction mechanism between the RLF procedure and BFR procedure is required for better system performance to reduce mismatch of the two separate procedures in different sublayers.